Methods for transmitting a digital terrestrial broadcast are different for each country. For example, the frame of a digital terrestrial broadcast (DTMB: Digital Terrestrial Multimedia Broadcast) in China is composed of a frame header (FH) which is a known signal and a frame body (FB) which is a subsequent data signal.
Since the FB does not have a mechanism for removing inter-symbol interference (in the case of DTMB, inter-frame interference) such as a guard interval used in many OFDM (Orthogonal Frequency Division Multiplexing) systems, interference due to delay waves in a multi-path channel becomes a problem.
In order to eliminate this problem, a technique has been proposed in which a frame header portion (hereinafter, FH portion), which is a known signal, is removed based on a channel estimate, and the last (or first) portion of a data signal is added to the beginning (or end) to restore the cyclicity of the data signal, thereby enabling demodulation without inter-frame interference.
With this technique, inter-frame interference due to the multi-path channel can be eliminated, but if the maximum delay time of the delay waves exceeds the FH length, inter-frame interference from the adjacent frames occurs. This interference occurs at a constant ratio relative to the desired signal component regardless of the power of the dominant wave and delay wave, and thus no matter how small the power of the delay wave is, if the delay time is large, a large interference will occur.